This invention is directed towards providing a self-venting cap for releasing vapor pressure from sealed containers. Pressure can accumulate in containers from a variety of causes including gas evolving chemical reactions, de-gassing of filled contents, foaming of contents from normal shipping and handling, temperature fluctuations, attitudinal changes, as well as abnormal conditions which may result from contamination or mishandling of the containers.
There is a particular demand for venting closures for retail containers of surfactants, cleaning products, and similar fluids which tend to generate vapor pressure. As pliable, plastic containers have become more popular with consumers, vapor pressure problems have become more numerous. Such problems include failed closures, container distortion which interferes with retail displays, and consumer distrust of misshapen (pressure distorted) containers. Packaging volumes are often less efficient as product head space, the unfilled volume, is increased to compensate for pressure fluctuations.
A variety of ventable caps and containers are known in the art. Several patents exist which provide for a gas-permeable, liquid-impermeable polytetrafluorethylene (PTFE) barrier for venting vapor pressure. One such patent is U.S. Pat. No. 3,951,293 to Schulz which is incorporated herein by reference and which discloses a liquid closure having one or more horizontal film layers of PTFE as a cap liner. The liner permits communication between the container vapor pressure and the external vapor pressure through a perforated cap or sealing diaphragm. While such a closure is suitable for many applications, it has been found unsuitable for some viscous liquids. Further, the prior art designs require generous use of the PTFE material to provide sufficient venting. Therefore, there is room for variation and improvement within the art.